The present invention relates to a high-sensitivity photopolymerization initiator for producing a color filter; to a high-quality photosensitive coloring composition for producing a color filter, which can be developed with a solvent or an aqueous alkaline solution after irradiation with UV light; to a color filter which is used in devices such as a solid state pick-up device and a liquid crystal display device; and to a method for producing the color filter.
In recent years, demand has arisen for a color filter used in a device such as a liquid crystal display device, where the filter is thin and defect-free; has properties such as heat and light resistance; and has optical properties such as high transparency and high contrast in accordance with the trend toward reducing the thickness and increasing the width of the device. In addition, increase of the yield of a production step and reduction in the number of production steps are more and more required, along with a demand for reducing production cost of a color filter. A color filter per se comprises a transparent substrate such as a glass plate on which fine stripes of two or more hues are disposed in a parallel or crossing manner or fine pixels are disposed in lateral and longitudinal directions in a predetermined pattern. Each pixel has a fine shape and a dimension of some 10 xcexcm to some 100 xcexcm, and the pixels for each hue must be arrayed according to a predetermined order. Thus, a variety of methods for producing a color filter have been proposed. Of these, from many viewpoints, such as the precision of the produced filter and production cost, a pigment-dispersion method employing a photosensitive coloring composition in which a pigment is dispersed has gained wide acceptance.
The pigment-dispersion method comprises applying, on a substrate, a photosensitive coloring composition containing a pigment, a resin serving as a matrix, and a cross-linking agent; and forming each coloring layer in a predetermined pattern through photolithography. More specifically, a color filter is produced through the following steps: applying the aforementioned photosensitive coloring composition for achieving one filter color on a transparent substrate such as a glass plate; exposing patternwise; developing the unexposed portion with a solvent or an aqueous alkaline solution to thereby form a pattern of a first color; and sequentially repeating the procedure for another filter color. A negative-type photosensitive coloring composition is predominantly employed as the above described coloring composition, in view of properties of the produced color filter and a wide range of usable materials. Currently, during development, a solvent is used very seldom, from the viewpoints of environmental problems; instead, an aqueous alkaline solution is predominantly used. Exposure is typically carried out by use of UV light. In the above production steps, only a predetermined portion is irradiated with light such as UV light, to thereby cause a chemical reaction; i.e., radical polymerization, exclusively in the exposed portion.
Since a negative-type photosensitive composition predominantly undergoes radical polymerization, the sensitivity of the composition may be reduced through inhibition of polymerization caused by oxygen in the air. In order to solve this problem, for example, the applied photosensitive composition is irradiated with light after an oxygen-shielding film such as a poly(vinyl alcohol) film is formed on the composition. However, recently, demand has arisen for a photopolymerization initiator for producing a color filter, where the initiator has such high sensitivity that additional treatment such as the provision of an oxygen-shielding film can be eliminated.
In this connection, Japanese Patent Application (kokai) No. 6-201913 discloses a photopolymerization initiator comprising solely a triazine compound, and a photopolymerization initiator comprising a triazine compound and an imidazole compound in combination. Japanese Patent Application (kokai) No. 10-253813 discloses a photopolymerization initiator comprising a polyfunctional thiol compound and at least one compound selected from a biimidazole compound, a titanocene compound, a triazine compound, and an oxadiazole compound. Photopolymerizable compositions containing these photopolymerization initiators for achieving red, green, and blue colors have a certain degree of sensitivity. However, a photopolymerizable composition for achieving a black color, particularly a photopolymerizable composition containing a black pigment, has drawbacks, such as a considerable reduction in sensitivity due to a shielding effect of the black pigment during exposure, increase of exposure time, and insufficient curing, even when the composition contains the above-described polymerization initiator.
The present inventors have found that a photopolymerization initiator comprising a sensitizer (A) which absorbs light having a wavelength of 300-500 nm, an organic boron complex (B), and a thiol-group-containing compound (C) is suitable for producing a color filter, and that the above problems are solved by use of the initiator. The present invention has been accomplished on the basis of this finding.
In view of the foregoing, an object of the present invention is to provide a high-sensitivity photopolymerization initiator for producing a color filter.
Another object of the present invention is to provide a photosensitive coloring composition containing the initiator.
Another object of the present invention is to provide a color filter exhibiting excellent resistance to a variety of phenomena.
Another object of the present invention is to provide a method for producing the color filter.
Accordingly, the present invention provides a photopolymerization initiator for producing a color filter comprising a sensitizer (A) which absorbs light having a wavelength of 300 to 500 nm; an organic boron complex (B) represented by formula (1): 
wherein each of R1, R2, R3, and R4 represents an alkyl group, an aryl group, an aralkyl group, an alkenyl group, a heterocyclic group, or an alicyclic group; and Z+ represents an ammonium cation, a sulfonium cation, an oxosulfonium cation, a pyridinium cation, a phosphonium cation, an oxonium cation, or an iodonium cation; and a thiol-group-containing compound (C).
Preferably, the thiol-group-containing compound (C) is at least one species selected from 2-mercaptobenzothiazole, trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), and pentaerythritol tetrakis(3-mercaptopropionate).
Preferably, the sensitizer (A) contains a benzophenone compound and/or a biimidazole compound.
The present invention also provides a photosensitive coloring composition for producing a color filter, which comprises a transparent polymer (D) soluble in a solvent or an aqueous alkaline solution, a compound having an ethylenic unsaturated bond (E), a pigment (F), and the above-described photopolymerization initiator.
The present invention also provides a color filter having pixels fon-ned on a transparent substrate by use of the photosensitive coloring composition.
The present invention also provides a method for producing a color filter comprising forming a layer of the photosensitive coloring composition on a transparent substrate and photocuring exposed portions of the layer of the composition through exposure.
The present invention will next be described in more detail. When R1, R2, R3, and R4 in formula (1) represent alkyl groups, and the alkyl groups may have substituents. Specifically, a C1-C12 linear or branched alkyl group which may have a substituent is preferred. Examples of suitable alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-octyl group, a dodecyl group, a cyanomethyl group, a 4-chlorobutyl group, a 2-diethylaminoethyl group, and a 2-methoxyethyl group.
When R1, R2, R3, and R4 in formula (1) represent aryl groups, the aryl groups may have substituents. Specifically, the groups are aryl groups which may be substituted. Examples of suitable aryl groups include a phenyl group, a tolyl group, a xylyl group, a mesityl group, a 4-methoxyphenyl group, a 2-methoxyphenyl group, a 4-n-butylphenyl group, a 4-tert-butylphenyl group, a naphthyl group, a 4-methylnaphthyl group, a 4-ethylnaphthyl group, an anthryl group, a phenanthryl group, a 4-nitrophenyl group, a 4-trifluoromethylphenyl group, a 4-fluorophenyl group, a 4-chlorophenyl group, and a 4-dimethylaminophenyl group.
When R1, R2, R3, and R4 in formula (1) represent aralkyl groups, the aralkyl groups may have substituents. Specifically, the groups are aralkyl groups which may be substituted. Examples of suitable aralkyl groups include a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, and a 4-methoxybenzyl group.
When R1, R2, R3, and R4 in formula (1) represent alkenyl groups, the alkenyl groups may have substituents. Specifically, the groups are alkenyl groups which may be substituted. Examples of suitable alkenyl groups include a vinyl group, a propenyl group, a butenyl group, and an octenyl group.
When R1, R2, R2, and R4 in lormula (1) represent heterocyclic groups, the heterocyclic groups may have substituents. Specifically, the groups are heterocyclic groups which may be substituted. Examples of such heterocyclic groups include a pyridyl group, a 4-niethylpyridyl group, a quinolyl group, and an indolyl group.
When R1, R2, R3, and R4 in formula (1) represent alicyclic groups, the alicyclic groups may have substituents. Specifically, the groups are alicyclic groups which may be substituted. Examples of such alicyclic groups include a cyclohexyl group, a 4-methylcyclohexyl group, a cyclopentyl group, and a cycloheptyl group.
When Z+ in formula (1) represents an ammonium cation, examples thereof include a tetramethylammonium cation, a tetraethylammonium cation, a tetra-n-propylammonium cation, a tetra-n-butylammonium cation, an n-butyltriphenylammonium cation, a tetraphenylammonium cation, and a benzyltri-phenylammonium cation.
When Z+ in formula (1) represents a sulfonium cation, examples thereof include a triphenylsulfonium cation, a tri(4-tolyl)sulfonium cation, and a 4-tert-butylphenyldiphenylsulfonium cation.
When Z+ in formula (1) represents an oxosulfonium cation, examples thereof include a triphenyloxosulfonium cation, a tri(4-tolyl)oxosulfonium cation, and a 4-tert-butylphenyldiphenyloxosulfonium cation.
When Z+ in formula (1) represents an oxonium cation, examples thereof include a triphenyloxonium cation, a tri(4-tolyl)oxonium cation, and a 4-tert-butylphenyldiphenyloxonium cation.
When Z+ in formula (1) represents a pyridinium cation, examples thereof include an N-methylpyridinium cation and an N-n-butylpyridinium cation.
When Z+ in formula (1) represents a phosphonium cation, examples thereof include a tetramethylphosphonium cation, a tetra-n-butylphosphonium cation, a tetra-n-octylphosphonium cation, a tetraphenylphosphonium cation, and a benzyltriphenylphosphonium cation.
When Z+ in formula (1) represents an iodonium cation, examples thereof include a diphenyliodonium cation, a di(4-methylphenyl)iodonium cation, and a di(4-tert-butylphenyl)iodonium cation.
Examples of organic boron complexes represented by formula (1) include tetramethylammoniurm n-butyltriphenylborate, tetraethylammonium isobutyltriphenylborate, tetra-n-butylammonium methyltriphenylborate, tetra-n-butylammonium n-butyltriphenylborate, tetra-n-butylammonium n-octyl-triphenylborate, tetra-n-butylamrnmonium n-butyltri(4-tert-butyl-phenyl)borate, tetra-n-butylammonium methyltrinaphthylborate, tetra-n-butylammonium n-butyltrinaphthylborate, tetra-n-butylammonium n-octyltrinaphthylborate, tetra-ti-butylammonium methyltri(4-methylnaphthyl)borate, tetra-n-butyl-ammonium n-butyltri(4-methylnaphthyl)borate, tetra-n-butylammonium n-octyltri(4-methylnaphthyl)borate, triphenylsulfonium n-butyltriphenylborate, triphenyl-sulfonium n-butyltrinaphthylborate, triphenyloxosulfonium n-butyltriphenylborate, triphenyloxosulfonium n-butyltrinaphthylborate, triphenyloxonium n-butyltriphenylborate, N-methylpyridinium n-butyltriphenylborate, tetraphenyl-phosphonium n-butyltriphenylborate, and diphenyliodonium n-butyltriphenylborate.
In general, the organic boron complex represented by formula (1) absorbs substantially no light having a wavelength of 300 nm or longer. Thus, when the complex is used alone, it is not sensitive to light from a typical UV lamp. However, the combination of the complex and a sensitizer has remarkably high sensitivity.
In the present invention, the organic boron complex (B) is incorporated typically in an amount of 1 to 60 wt. % based on the compound having ethylenic unsaturated bonds, preferably 5 to 30 wt. %. When the amount of the organic boron complex is insufficient, polymerization proceeds insufficiently, whereas when the amount is present in excess, the stability of the composition may decrease, to thereby cause an economically disadvantageous situation.
Examples of the sensitizer (A) which absorbs light having a wavelength of 300 to 500 nm used in the invention include a photopolymerization initiator, a sensitizer, and a dye absorbing light having a wavelength in the range. Examples of the sensitizers include cationic dyes; benzophenones; acetophenones; benzoins; thioxanthones; imidazoles; biimidazoles; coumarins; ketocoumarins; triphenylpyryliums; triazines; benzoic acids; and maleimides. In addition, acylphosphine oxide, methyl phenyl glyoxylate, an xcex1-acyloxime ester, benzil, camphorquinone, and ethylanthraquinone may also be employed. These compounds may be used alone or as a combination of two or more thereof.
Specific examples of the sensitizers include cationic dyes such as Basic Yellow 1, 11, 13, 21, 28, 29, 36, 51 and 63, Basic Orange 21 and 22, benzophenone, 4-methylbenzophenone, 4-fluorobenzophenone, 4-chlorobenzophenone, 4-bromobenzophenone, 4-morpholinobenzophenone, 4-dimethylaminobenzophenone, 4,4xe2x80x2-bis(dimethylamino)benzophenone, 4,4xe2x80x2-bis(diethylamino)benzophenone, 4-dimethylaminoacetophenone, 4-diethylaminoacetophenone, 2-hydroxy-2-phenylacetophenone, 2,4-diethylthioxanthone, 2-methylthioxanthone, N-methylimidazole, N-phenylimidazole, 2,2xe2x80x2-bis(2-chlorophenyl)-4,4xe2x80x2,5,5xe2x80x2-tetraphenyl- 1,2xe2x80x2-biimidazole (hereinafter referred to as HIABI), 2,2xe2x80x2-bis(2-chlorophenyl)-4,4xe2x80x2, 5,5xe2x80x2-tetra(ethoxyphenyl)- 1,2xe2x80x2-biimidazole, 2,2xe2x80x2-bis(2-chlorophenyl)-4,4xe2x80x2,5,5 xe2x80x2-tetra(4-bromophenyl)-1,2xe2x80x2-biimidazole, 2,2xe2x80x2-bis(2,4-dichlorophenyl)-4,4xe2x80x2,5,5xe2x80x2-tetraphenyl-1,2xe2x80x2-biimidazole, 2,2xe2x80x2-bis(2-chlorophenyl)-4,4xe2x80x2,5,5xe2x80x2-tetra(3-methoxyphenyl)-1,2xe2x80x2-biimidazole, 2,2xe2x80x2-bis(2-methylphenyl)-4,4xe2x80x2,5,5xe2x80x2-tetraphenyl-1,2xe2x80x2-biimidazole, coumarin, 7-diethylaminocoumarin, ethyl 4-dimethylaminobenzoate, N-methylmaleimide, and N-phenylmaleimide. These compounds may be used alone or as a combination of two or more thereof. Considering stability of the initiator and a composition and ability to initiate polymerization, benzophenone compounds, benzoic acids, and biimidazole compounds are preferably used.
In the present invention, the sensitizer (A) which absorbs light having a wavelength of 300 to 500 nm is incorporated typically in an amount of 1 to 60 wt. % based on the compound having ethylenic unsaturated bonds, preferably 2 to 30 wt. %. When the amount is very low, the sensitizing effect may not be obtained, whereas when the amount is present in excess, the sensitizer absorbs light and thus light transmittance efficiency may become poor, and polymerization initiation efficiency may decrease, which is unsatisfactory.
The thiol-group-containing compound (C) used in the present invention is a thiol-group-containing compound in the molecule. Examples of suitable thiol compounds include 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, 5-chloro-2-mercaptobenzothiazole, 2-mercapto-5-methoxybenzothiazole, 5-methyl- 1,3,4-thiadiazole-2-thiol, 5-mercapto-1-methyltetrazole, 3-mercapto-4-methyl-4H-1,2,4-triazole, 2-mercapto-1-methylimidazole, 2-mercaptothiazoline, octanethiol, hexanedithiol, decanedithiol, 1,4-dimethylmercaptobenzene, butanediol bis(2-mercaptoacetate), butanediol bis(3-mercaptopropionate), ethylene glycol bis(2-mercaptoacetate), ethylene glycol bis(3-mercaptopropionate), trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), and trishydroxyethyl tris(3-mercaptopropionate). In considering polymerization initiation ability, particularly, 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercapto-acetate), and pentaerythritol tetrakis(3-mercaptopropionate) are preferred. These compounds having a thiol group may be used alone or as a combination of two or more thereof.
In the present invention, the thiol-group-containing compound (C) is incorporated typically in an amount of 1 to 60 wt. % based on the compound having ethylenic unsaturated bonds, preferably 5 to 30 wt. %. When the amount is insufficient, polymerization may not be effectively initiated, whereas when the amount is present in excess, the initiation performance may not increase and the addition disadvantageously affects the properties of the cured product.
In the present invention, the combination of the sensitizer (A) which absorbs light having a wavelength of 300 to 500 nm, the organic boron complex (B) represented by formula (1), and the thiol-group-containing compound (C) enhances polymerization performance.
The transparent polymer (D) which is soluble in a solvent or an aqueous alkaline solution used in the present invention is a polymer with high transparency. Accordingly, a film formed of the polymer having a thickness of 1 xcexcm preferably has a percent transmission of 80% or more, more preferably 95% or more within a visible range of 400 to 700 nm, and the polymer can be dissolved in a developer (a solvent or an aqueous alkaline solution). Examples of the polymer include thermosetting resins, thermoplastic resins, and photosensitive resins. These polymers may be used alone or as a combination of two or more thereof. In a post-treatment process for producing a color filter, the polymer is treated at high temperature or with a variety of solvents and chemicals, and therefore, the transparent polymer (D) having excellent heat resistance and resistance to solvents and chemicals is preferably used.
The compound (E) having ethylenic unsaturated bonds used in the present invention may be a compound which can undergo radical polymerization (or cross-linking) and is typically called a monomer or oligomer. Examples of suitable compounds include (meth)acrylic acid; (meth)acrylic acid esters such as methyl (meth)acrylate, butyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; ethylene glycol di-(meth)acrylate; pentaerythritol tri(meth)acrylate; styrene; divinylbenzene; (meth)acrylamide; vinyl acetate; N-hydroxymethyl(meth)acrylamide; dipentaerythritol hexaacrylate; melamine acrylate; and an epoxy acrylate pre-polymer. Considering exposure sensitivity and resistance to a variety of phenomena after curing, multifunctional (meth)acrylic monomers are preferably used.
As used herein, the term xe2x80x9c(meth)acryxe2x80x9d refers to both xe2x80x9cmethacryxe2x80x9d and xe2x80x9cacry.xe2x80x9d
Widely used hues of color filters include additive color mixing types such as red, green, and blue; subtractive color mixing types such as cyan, magenta, and yellow; and black used in a black matrix portion. Coloring agents include dyes and pigments, but pigments are used in the present invention considering heat-resistance and photo-resistance as described above. In order to obtain suitable spectra, two or more pigments are used in combination. For example, a blue spectrum is obtained from the combination of a cyan pigment and a violet pigment; a green spectrum is obtained from the combination of a blue pigment and a yellow pigment; and a red spectrum is obtained from the combination of a red pigment and a yellow or an orange pigment.
Examples of the pigment (F) used in the present invention, represented by color index numbers, include C. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 55, 83, 86, 93, 109, 110, 117, 125, 137, 139, 147, 148, 153, 154, 166, 168, C. I. Pigment Orange 36, 43, 51, 55, 59, 61, C. I. Pigment Red 9, 97, 122, 123, 149, 168, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 240, C. I. Pigment Violet 19, 23, 29, 30, 37, 40, 50, C. I. Pigment Blue 15, 15:1, 15:4, 15:6, 22, 60, 64, C. I. Pigment Green 7, 36, C. I. Pigment Brown 23, 25, 26, C. I. Pigment Black 7, and Titanium Black.
In the photosensitive coloring composition of the present invention, the pigment should be sufficiently dispersed. In addition, the photosensitive coloring composition should be applied to a transparent substrate to a thickness of 1 to 3 xcexcm. Therefore, in order to impart suitable applicability to the composition, in general, the viscosity of the composition is controlled by use of a solvent. Examples of suitable solvents include methanol, ethanol, toluene, cyclohexane, isophorone, cellosolve acetate, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, xylene, ethylbenzene, methyl cellosolve, ethyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, isoamyl acetate, ethyl lactate, methyl ethyl ketone, acetone, and cyclohexanone. These solvents may be used alone or as a combination of two or more thereof.
The photosensitive coloring composition is produced by use of any of a variety of means for dispersion, such as a three-roll mill, a two-roll mill, a sand mill, an attrition mill, a ball mill, a kneader, and a paint shaker. In order to prevent gelation attributed to polymerization during the dispersion process, a polymerization inhibitor may be added, and a monomer and the photopolymerization initiator may be added after dispersion of the pigment. Furthermore, in order to facilitate the dispersion of the pigment, an appropriate dispersing aid may be added. Since a dispersing aid facilitates dispersion and prevents re-aggregation of the pigment, a color filter of excellent transparency can be produced.
In general, the color filter of the present invention is produced by applying the photosensitive coloring composition of the present invention to a transparent substrate such as a glass substrate, and photocuring the composition through exposure. In general, the color filter is produced by the following steps:
in a first step, a photosensitive color resin layer is formed on a transparent substrate;
in a second step, the photosensitive resin layer is exposed patternwise via a pattern mask having a specific pattern;
in a third step, the photosensitive color resin layer is developed after completion of patternwise exposure, to thereby retain the patterned photosensitive resin layer serving as a pixel layer on the transparent substrate; and
in a fourth step, the transparent substrate on which a pixel layer is formed is baked (post-baked) after completion of development. A method for producing the color filter of the present invention is not limited to the above-described method so long as the photosensitive coloring composition of the present invention is used.
Preferred steps for producing a color filter in the present invention will next be described in detail.
In the first step, the photosensitive coloring composition is applied to a transparent substrate such as a glass substrate through a coating method such as spray-coating, spin-coating, roll-coating, or screen-coating. In order to impart suitable fluidity to such a coating apparatus, the photosensitive coloring composition may contain, in addition to the aforementioned solvents, extender pigments such as barium sulfate, calcium carbonate, and silica; and a small amount of silicon-type or fluorine-type surfactants serving as leveling agents or defoaming agents. The applied photosensitive coloring composition may be dried (pre-baked) typically at 30 to 100xc2x0 C. for 10 to 30 minutes so as to remove solvent by use of a blower-equipped oven or a hot plate. When the temperature is very high or the drying time is very long, partial polymerization or cross-linking may occur and the solubility of unexposed portions to a developer may decrease, which disadvantageously causes poor development.
In the second step, the photosensitive resin layer obtained in the first step is irradiated with a UV beam via a photomask typically having a color filter pattern. A light source such as an ultra-high-pressure Hg lamp or a metal halide lamp is typically employed. Since UV light passing through the photomask typically has a wavelength of 300 nm or more, three types of rays included in the bright line spectrum of the ultra-high-pressure Hg lamp; i.e., i-ray (365 nm), h-ray (405 nm), and g-ray (436 nm), are used for polymerization or cross-linking. Therefore, sensitivity to the above three spectral lines is important when the photosensitive coloring composition is used in forming a color filter.
In the third step, the exposed photosensitive resin layer obtained in the second step is developed with a weak alkaline developer; i.e., the unexposed (uncured) portion of the photosensitive resin layer is removed so as to provide a pixel layer.
In the fourth step, the pixel-layer-formned transparent substrate obtained in the third step is post-baked at 160 to 300xc2x0 C. for about 20 to 60 minutes, to thereby obtain a pixel layer of a first color.
Beyond the first color, color filters of a variety of colors are produced by repeating the above four steps.